The overall objective of the proposed studies is to better understand the etiology of autoimmune hemolytic anemia (AIHA) leading eventually to more rational patient management and therapy. AIHA may be idiopathic or develop as a complication of a variety of disorders. The heterogeneity of RBC autoantibodies in these clinical conditions as well as those present in the plasma of healthy individuals remains poorly defined. The proposed studies will examine the human B-cell repertoire in benign versus pathologic RBC autoantibodies and determine whether particular antibody producing clones play an important role in the expression of autoimmune hemolytic disease. RBC specific human B-cell clones will be established from patients with AIHA as well as from healthy individuals by EBV transformation and somatic hybridization techniques. These B- cell clones will be characterized with respect to: 1) The structure and function of their Ig product (isotype, subclass, isoelectric point, and specificity); 2) Their karyotype, surface phenotype and Ig gene rearrangements; and, 3) Their immunoglobulin variable region genes by serological methods (with antiidiotypes) and by molecular methods (cDNA sequencing of Ig variable regions; usage of VH and VL subgroups with cDNA probes).